The objective of this project is to describe and assess mechanisms of breeding behavior in a natural animal population, with the aim of using the information gathered to better understand similar decision-making processes used by human beings. Humans and other animals make decisions concerning where to engage in different activities and these decisions affect subsequent choices of mates, dwelling and reproductive areas, escape routes, and foraging areas. Since the "mental health" and well-being of an organism may reflect the effectiveness of these decision-making processes, there is strong reason to believe that enlarging our pool of knowledge concerning mechanisms of decision-making about crucial life factors, such habitats, mates, and territories, will eventually contribute to clinical knowledge and treatments. Specifically, the study is based on monitoring site selection, territoriality, and reproductive success in a large, color-marked population of Red-winged Blackbirds, supplemented by data on breeding Yellow-headed Blackbirds on the same study area. This long-term monitoring of known individuals, combined with manipulative experiments that would be impossible with humans, will provide data on how males obtain breeding territories and what information they use to maximize their chances of becoming territorial or to acquire higher quality territories. In addition, field monitoring of blood hormone levels of territorial and non- territorial males, will reveal how hormonal states influence behavior during the breeding season and how behavior, in turn, influences hormone levels.